كُمُ

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – كُمُ is a noun

A noun may either be 1) Definite or indefinite 2) Masculine or feminine 3) Singular, dual or plural 4) Nominative, accusative, genitive or fixed

كُمُ is a suffix (a word added to the back of a word) of the second person of the personal and possessive pronoun, masculine, plural

Grammatical analysis of كُمُ
ضَمِيْرٌ مُتَّصِلٌ مَبْنِيٌّ عَلَى  السُّكُوْنِ
كُمُ is كُمْ with a dammah replacing the sukoon due a definite noun succeeding it in the sentence 
مَعْرِفَةٌجَمْعٌمُذَكَّرٌمَنْصُوْبٌ مَجْرُوْرٌالْمُخَاطَبُضَمِيْرٌمَبْنِيٌّاِسْمٌضَمِيْرٌ مُتَّصِلٌ
DefinitePluralMasculineAccusativeGenitiveYou’llPronounFixedNounAttached pronoun
Yours
 
Surah/Below are verses in the holy Quran containing the suffixكُمُ
Verse
102-1The mutual desire for piling up (abundance) distracts/ delights/ preoccupies youأَلْهَاكُمُ التَّكَاثُرُ